Conventional typewriter keyboards were originally designed with the so-called QWERTY key layout, incorporating the letters of the alphabet (A-Z) and four punctuation symbols (, . ; /). These keys were arranged in three rows, each row having ten keys. The letters were arranged on the keys so as to minimize the possibility of mechanical arms striking one another when frequently used keys were typed. At a later date, number keys (0-9) were added in a fourth row above the letter and punctuation keys. This keyboard eventually became known as the Universal Keyboard. With the addition of a space bar beneath the lowest row of keys, the Universal Keyboard comprised the typical keyboard for which typing manuals were devised to allow speed typing by touch.
Typists trained on the Universal Keyboard can achieve extremely high typing speeds by touch-typing memorized keystrokes. Because the keys are spaced in a small group, the position of the hands need not be changed, and high typing speeds can be maintained.
The rapid growth of small and mid-sized computers, supplemented by word processing programs, has largely replaced the conventional typewriter in the modern office. Typical keyboards for such computers have many non-touch-type keys in addition to the original touch-type keys of the Universal Keyboard. For example, one very popular type of personal computer has 101 keys. The touch-type keys are positioned in a group in the center of the keyboard. To the immediate left of this group are the Control key, Shift key, Alternate key, and Caps Lock key. To the immediate right of the touch-type keys are the Enter key, a Shift key, and a duplicate set of Control and Alternate keys. Further to the right are a set of cursor movement keys, editing keys, and a numeric keypad. To the left of the universal keyboard area is a two-column-by-five-row array of function keys (F1-F10).
These additional non-touch-type keys are necessary for proper operation and full utilization of the various features of modern computers. However these keys greatly reduce the speed with which computers can be operated, because the positions of these additional keys force the typist to break his or her touch-type routine, and slow to a greatly reduced typing speed. For example, to execute the command "Control-p", the left hand must be lifted away from the letter keys in order to hold down the Control key while the `p` key is typed with the right hand. Thus, the Control key, one of the most frequently used keys on the keyboard, is impossible to touch-type.
Many computers utilize a keyboard that is physically separate from the computer, and is connected thereto by a cable that includes a clock line and a data line. Pressing a key on the keyboard generates an eight-bit "make" code which is transmitted serially over the data line to the computer. Releasing the key generates a corresponding eight-bit "break" code which is sent over the data line after the make code. The clock line synchronizes the transmission of the make and break codes with the computer's on-board clock. The keyboard sends a data bit, and the computer reads the bit sent, every time the clock line goes low. In this way, the data is transmitted synchronously with the computer clock.
The first seven digits of the make or break code identifies the key which has been pressed or released. The eighth (most significant) bit of the code indicates whether the key is pressed (a make code) or released (a break code). For example, the letter A on the keyboard is represented by the seven bits 0011110. The eighth and most significant bit is `0` if the code is a make code, or `1` if the code is a break code. The computer holds the data line low while a data word is processed, and only allows the data line to go high when it is ready to receive another eight-bit word.
The computer usually generates a character on its display (such as a CRT screen) when a make code is received. The break codes only come into play when the "null" keys, such as the Control, Alternate, or Shift keys are used. These null keys do not generate a character or space when pressed, but only cause the computer to perform a function if the make code of such a key is immediately followed by the make code of a different key. For example, if the Control key make code is immediately followed by the Control key break code (i.e. the Control key is simply pressed and released), no discernable operation takes place. However, if the `t` key is pressed while the Control key is held down (Control key make code, followed by `t` key make code) then the computer will perform the "Control-t" command.
The use of make and break codes in keyboards of this type has made it possible in the present invention to make touch-type keys, such as the space bar and letter keys, perform the functions of the non-touch-type keys, by monitoring the sequence in which the keys are pressed and released.